Method for polishing metallographic specimens

ABSTRACT

A metallographic specimen is moved in a figure-of-eight motion over a stiff paper supported by a hard backing surface on which the polishing compound is positioned at the crossover point of the figure-of-eight motion. The specimen is rotated about its axis after each predetermined number of motions. Apparatus is provided to give a continuous range of selectable pressures between the specimen and paper.

United States Patent [72] inventors William F. Stuhrke; [50] Field of Search 51/281, Charles R. Underwood, Dayton, Ohio 283, I51, 154, 157 [2]] Appl. No. 889,863 221 Filed Dec. 19, 1969 References Cited Division of Ser. No. 730,831, UNITED STATES PATENTS y 21, 1968 l,257,047 2/1918 Suverkrop 51/64 [45] Patented May 4,1971 I W 3,305,976 2/l967 Koskie 51/151 [73] Assignee Said Underwoodassor. to the United States of America as represented by the Secretary Pnmary Exammer l'ester Swmgle, of the Force Attorneys-Harry A. Herbert, Jr and Richard J. K1lloren ABSTRACT: A metallographic specimen is moved in a figureof-eight motion over a stiff paper supported by a hard backing [54] METHOD FOR POLISHING METALLOGRAPHIC surface on which the polishing compound is positioned at the SPEQIMENS crossover point of the figure-of-eight motion. The specimen is 2 Clams Drawmg 5- rotated about its axis after each predetermined number of mo- [52] US. Cl 51/281 tionspp r is p i to give a c ntinuous range of [51] Int. B24b 1/00 selectable p r s en he pe imen and paper.

79 7a 5J5, 47 33 I2 7 68 u x as I 72 7a 0 s4 8 T a s7 s.

54 55 l 52 "Ia-o:- I 10h! l a o n GIRE X P TENIED MAY 4197: 3577.689

. BACKGROUND OF THE INVENTION In prior art polishing systems for metallographic specimens,

large amounts of expensive polishing compound have been required to obtain suitable specimens. When a large amount of polishing compound is used a certain amount of agglomeration takes place which leads to deep scratches in the specimen surface. Also, with prior art systems, some contamination takes place between the different compounds when changes are made from one grade to another.

There is no acceptable apparatus available in the prior art for preparing metallographic specimens of extreme hardness differences such as with aluminum reinforced with boron filaments.

SUMMARY OF THE INVENTION According to this invention the specimen is moved -in a tigure-of-eight pattern over a stiff sheet of paper which is sup ported on a hard backing surface. A small amount of the polishing compound, such as diamond dust or silicon carbide in oil, is placed in the normal path of movement of the specimen preferably at the crossover point in the figure-ofeight pattern and is spread out by the motion of the specimen in a very thin layer over the entire pattern on the sheet of paper. This requires about 1/500th of the amount of compound used in prior art devices and eliminates the agglomeration problem. By cleaning the specimen and discarding the sheet of paper used, contamination can be eliminated when changing from one grade of compound to the next. Means are provided to vary the pressure over a continuous range to include levels substantially below the capability of existing machines, so that improved results can be obtained in polishing metallographic specimens.

Vibration is substantially eliminated in the apparatus by the use of an air bearing and a massive support for the specimen holder.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a .specimenpolishing apparatus according to the invention;

FIG. 2 is an enlarged left end view of the polishing apparatus of the device of FIG. 1;

FIG. 3 is a sectional view of the device of FIG. 2 along the line 34;

FlG. 4 is an enlarged cutaway top view of the polishing arm for the device of FIG. 1; and

'FlG. 5 is a sectional 'view of the polishing arm of FIG. 4 along the line 55.

DESCRIPTION OF THE PREFERRED EMBODIMENT Reference is now made to FIG. 1.of the drawing which shows a metallographic specimen polishingapparatus 10, having a support structure 12 secured to a base member 14. The support structure 12 has a recessl6 therein. A hard support plate 18, of a material such as granite, is positioned in the recess 16 with a chamber 19 beneath the plate 18. A plurality of holes 20 are bored in the plate 18. A sheet of stiff paper 22 is positioned over plate 18 and is retained by means of a vacuum in space 19 acting through holes 20 and provided by means of a vacuum pump 24 and a flexible tube 25 intercon-;

necting the pump 24 and chamber 19 to provide a vacuum in chamber 19 of about 25 microns of mercury. The vacuum level given is merely by way of example as the exact vacuum would be determined by the particular structure.

A-specimen holder assembly 30 is held by a support arm 31 which, in turn, is supported by support structure '33. The support structure 33 is secured at 35 to a platform 37.

The platform 37 is positioned above an air bearing base member 38 which is secured to base member 14. The platform 37 has a recess 39 with a metal plate41 of a material such as stainlessnsteel closing the recess and providing a chamber 43 within the platform 37. The plate 41 has a plurality of holes 44 therein and may be secured to platform 37 by welding or with an adhesive. Air at a pressure of about 30 p.s.i. from supply 46 is supplied to, chamber 43, through aflexible member 47, to raise the platform 0.005 to 0.006 inch. from member 38 and provide an air bearing between the platform 37 and the air bearing base member 38. The air pressure given is merely by way of example with the exact pressure being determined by the particular design of the air bearing and support'structure.

The platform 37 is moved over the air bearing base member 38 by means of two crank members 49 and 50 driven by a motor 52 through gear boxes 54 and 55. The gear ratio of gear boxes 54 and 55 are selected so that crank 49 rotates at twice the speed of crank 50. Crank 49 drives the platform 37 by means of a pair of slider bars 61 and 62, secured to platform 37 by supports 63 and 64, a slider 65 and linkage 66. Crank 50 drives the platform 37 by means of a pair of slider bars 67 and 68, secured to platform 37, by supports 70 and 71, a slider 72 and a linkage 74. The crank member 49 runs at twice the speed of crank member 50. By the use of elongated sliders 65 and 72, and because of the low frictional load of the air bearing, this drive arrangement was made to function without binding even though there is some torque on the sliders during operation.

cylinder 78 to which air is supplied from supply 46 through tubular member 79, pressure regulator 80 and a conventional rotary valve 81. The rotary valve 81 is driven by shaft 82 which also drives crank 50 so that the pawl 76 is operated after every predetermined number of revolutions of crank 50 in accordance with the ratio of pulleys 84 and 85, shown here to be i to l. i

The metallographic specimen to be polished is held in a conventional specimen holder 86 as the chuck shown. It is to be understood that other specimen holders than that shown may be used.

The pressure of the specimen against the paper is determined by the pressure of the air suppliedto air cylinder 87 which is controlled by valve 89 and gage 90 connected in line 91 from air supply 46. The pressure may be adjusted between 0 and 100 p.s.i. The tube 92 from gauge 90 is secured against rotation as ratchet wheel 78 is rotated by means of connection 93 to arm 31. A conventional seal 95 is provided around tube 1n the operation of the apparatus, 'vacuum pump 24 is turned on and a sheet of stiff paper 22, such as a'file' card, is positioned over support plate 18. The specimen is then secured in the specimen holder 86 and the desired pressure level is setby valve 89. A small amount of polishing compound is placed in the normal path of movement of the specimen but preferably at the crossover point of the figure-of-eight pattern on paper 22. The motor 52 is then started to movethe specimen over the paper in a figure-of-eight pattern 97. After each revolution of shaft 82, an impulse is supplied to air cylinder 79 to rotate the specimen a portion of one turn about its vertical axis. When it is desired to change to a difi'erent gradev of polishing compound, the machine is shut down, the paper 22 is replaced by another paper, the specimen is cleaned and replaced in the specimen holder, and the above described operation is repeated with the new grade of compound. There is thus provided an improved apparatus and method for polishing metallographic specimens. While a particular apparatus is shown and described, it is obvious that other apparatus could be provided without departing from the general principles and scope of the invention. Also. the method of the invention could be performed by manually moving the specimen in the figure-of-eight pattern over the paper.

. 3 I While paper has been described as the material for holding I the polishing material, asheet of -any disposable material having amat surface, including plastic, cloth and even some metals and glass may be used. A mat surface for this purpose is to be considered to be any surface that is not too smooth or shiny to retain the polishing compound Many other changes also can be made without departing from the general principles and scope of the invention.

We claim:

1. The method for polishing a metallographic specimen comprising; securing astiff sheet of disposable material having a mat surface onto a hard backing surface, moving the fraction of a turn after each predetermined number of cycles of the figure-of-eight motion.

2. The method as recited in claim 1 wherein the polishing material is applied to the disposable material at the position of the crossover in the figure-of-eight motion. 

1. The method for polishing a metallographic specimen comprising; securing a stiff sheet of disposable material having a mat surface onto a hard backing surface, moving the specimen over the disposable material in a figure-of-eight motion, applying a small amount of polishing material to the disposable material in the path of the motion of the specimen; adjusting the pressure of the specimen against the disposable material to a predetermined level, rotating the specimen about the specimen axis perpendicular to the disposable material a fraction of a turn after each predetermined number of cycles of the figure-ofeight motion.
 2. The method as recited in claim 1 wherein the polishing material is applied to the disposable material at the position of the crossover in the figure-of-eight motion. 